Expansion of bioenergy crops in the midwestern United States: implications for the hydrologic cycle under climate change

To meet emerging bioenergy demands, significant areas of the large-scale agricultural landscape of the Midwestern United States could be converted to 2nd generation bioenergy crops such as miscanthus and switchgrass. Their high biomass productivity in a longer growing season linked tightly to water use highlight the potential for significant impact on the hydrologic cycle in the region. This issue is further exacerbated by the uncertainty in the response of the vegetation under elevated CO2 and temperature. This study attempts to capture the eco-physiological acclimations of bioenergy crops under climate change and predict how hydrologic fluxes are likely to be altered from their current magnitudes. A mechanistic multilayer canopy-root-soil model is applied for capturing the emergent vegetation responses to environmental change. Observed data and Monte Carlo simulations of weather for recent past and future scenarios are used to characterize the variability range of the predictions. We found that, under present weather conditions, miscanthus and switchgrass utilized more water than maize for total seasonal evapotranspiration by approximately 58% and 36%, respectively. Projected higher concentration of atmospheric CO2 (550 ppm) is likely to decrease water used for evapotranspiration of miscanthus, switchgrass, and maize by 12%, 10%, and 11%, respectively. However, when climate change with projected increases in air temperature and reduced summer rainfall are also considered, there is a net increase in evapotranspiration for all crops, leading to significant reduction in soil-moisture storage and specific surface runoff. These results highlight the critical role of the warming climate in potentially altering the water cycle in the region under extensive conversion of existing maize cropping to support bioenergy demand